1. Technical Field
The invention relates to a method and a device for measuring the protrusion of bearing shells.
2. Related Art
FIG. 1 shows a bearing shell 1, which is provided with a sliding surface 11, a bearing backing 12 and parting faces 10. In the drawing, a lubricating groove and lubricating apertures are shown in the sliding surface. The bearing shell 1 shown can be used, for example, as a connecting rod bearing.
The bearing shell 1 usually has a spread d3, as shown in FIG. 2, i.e. the diameter of the bearing shell 1 measured across the parting faces is greater than the bearing shell diameter d2 when the bearing shell (1) is fitted into a housing receptacle. This results in a good seating against the housing wall on assembly, so that the bearing shell 1 is prevented from falling out or rotating. The radius of the bearing shell 1 in the installed state, i.e. without the spread, is designated as the Q-value.
The bearing shell 1 also has a so-called “protrusion”. In FIG. 3, the protrusion is designated SN. The circumferential length of the bearing shell is greater than the circumferential length of the housing receptacle by the value of the protrusion SN. When the bearing shell 1 is installed, the circumferential length of the bearing is elastically shortened. The crush pressure thereby produced ensures the correct seating of the bearing. In FIG. 3, the bearing shell 1 is pressed into a measuring depression 20. Seen in relation to the measuring depression, the protrusion SN denotes, as a main feature of the bearing shell 1, the length by which the circumferential length of the bearing shell 1 exceeds that of the measuring depression 20 once the bearing shell 1 has been pressed into the measuring depression 20 with a bearing-specific application force FB. Dcb denotes the test seating diameter of the measuring depression. Since, for technical reasons, this main feature cannot be reliably manufactured, it must be tested according to the design specifications. Typical target values for the protrusion are 50 to 150 μm, with a tolerance of 10 to 30 μm.
According to the prior art method shown in FIG. 3, the bearing shell 1 is pressed into the bearing-specific measuring depression 20 by applying a defined inserting force at a defined approach speed. In the process, a form-fit with the solid, stiffly designed depression 20 is pursued. The length of the bearing shell 1 projecting beyond the edge of the measuring depression—the protrusion SN—is measured by contacting or non-contacting means.
The method described requires a high degree of accuracy from the measuring depression and a different measuring depression for each bearing shell type. Furthermore, frictional influences can have a disadvantageous effect on the measurement result and can affect the properties of the bearing shell.
Other methods or proposals from the prior art relate to circumference measurement with the aid of measuring bands stretched over the backing of the bearing or travelling along the backing using a frictional wheel. Possible stretching of the measuring bands or slippage of the frictional wheel can have disadvantageous effects on the measurement result. Wear of the measuring devices also has disadvantageous effects on the measurement result.
The methods described require relatively long cycle times. There is a need for an economical testing procedure which enables a reproducible, comparable and traceable measurement of the protrusion for a tolerance range of 10 to 30 μm, without a bearing-specific measuring depression, with a cycle time of less than 1 s.
DE 34 35 245 A 1 describes a method for determining the load-free protrusion value of a bearing shell. For this purpose, the elastic shortening of the protrusion is measured as a function of a test force applied to a parting face of the bearing shell.